Police have released details of the final movements of a couple critically ill in hospital after being exposed to novichok.

Dawn Sturgess, 44, and her partner Charlie Rowley, 45, were taken ill at a house in Amesbury, Wiltshire, on Saturday.

Tests later showed they had been exposed to novichok – the chemical weapon used in the attempted murders of ex-Russian spy Sergei Skripal and his daughter Yulia just eight miles away in Salisbury in March.

The Metropolitan Police says around 100 counter-terror officers are working “round the clock” alongside Wiltshire Police to identify the source of contamination.

Image:Investigators wearing hazmat suits enter the John Baker House hostel where Dawn Sturgess was staying

“Due to the unique challenges involved with this operation, police activity is expected to take weeks and months to complete,” the Met said.

“The focus of the investigation remains identifying the source of the contamination as quickly as possible.

“As part of this, detectives have been making a number of enquiries to trace the precise movements of the man and woman in the period prior to them falling ill.”

Image:The pair visited Amesbury Baptist Centre

Police have pieced together the following timeline of events:

Friday 28 June

12.20pm – Ms Sturgess and Mr Rowley are together at John Baker House – a supported housing scheme in Salisbury – about half an mile from the Zizzi restaurant where the Skripals dined before becoming ill.

They then leave and visit a number of shops in Salisbury before going to Queen Elizabeth Gardens.

4.20pm – They return to John Baker House.

10.30pm – They catch a bus to Amesbury.

Police say they believe the couple then spent the night at Muggleton Road, Amesbury.

Saturday 30 June

10.15am – South West Ambulance Service is called to Muggleton Road, where Dawn Sturgess is taken ill. Charlie Rowley is also present at the address.

Midday – Charlie Rowley visits a Boots chemist on Stonehenge Walk in Amesbury and then returns to Muggleton Road around half an hour later.

1pm – He visits the Amesbury Baptist Centre about a mile from the house.

3pm – He returns home.

6.20pm – The South West Ambulance Service is called back to the address on Muggleton Road and Mr Rowley is also taken to hospital.

Image:Charlie Rowley went to Boots after Dawn Sturgess was taken ill

Police say they have spoken to “several key witnesses” and are trawling through more than 1,300 hours of CCTV footage.

Officers in hazmat suits are investigating key locations in Amesbury and Salisbury, and the sites have been cordoned off as a precaution as “meticulous and systematic searches” take place.

Police said there was no evidence that Ms Sturgess and Mr Rowley visited any of the sites that were decontaminated following the attempted murders of Sergei and Yulia Skripal.

“We are not in a position to say whether the nerve agent was from the same batch that the Skripals were exposed to,” they said.